The invention relates to a device for controlling the filing of a depth gauge of a cutter link of a chain saw chain.
The cutter links or cutter teeth, as they are also known, of a standard chain saw chain include a depth gauge and a cutter edge separated by a space. The depth gauge preceeds the cutter edge in the direction of travel of the chain. The depth gauge should project outwardly slightly less than the cutter edge and thus determines the amount of material removed in each pass of each cutter edge. The amount of material removed is approximately the difference between the height of the depth gauge and the height of the cutter edge.
The cutter edge is normally sharpened by use of a round file. Devices have been developed for holding round files for sharpening saw chains as found in the U.S. Pat. Nos. 3,327,567 to Penberthy, 3,518,900 to Ehlen and 4,012,969 to Granberg. The latter shows an adjustable saw chain guide and holder.
A problem arises however when the cutter edge is sharpened. This reduces the height of the cutter edge so that the outward projection of the cutter edge is reduced relative to the depth gauge. This reduces cutting efficiency of the cutter link. The efficiency can be restored by filing the depth gauge until the proper relationship is restored. However, the depth gauge must not be filed too much or the cutting edge will take too deep a bit which increases the likelihood of kick back and potential serious injury to the user.
Devices have been developed for adjusting the relationship between the depth gauge and the cutter edge. An example is found in U.S. Pat. No. 3,796,113 to Granberg which shows a depth gauge attachment using a rotary grinder. The device rests on the tips of two adjacent cutting teeth. Unfortunately, this leads to inaccuracies because the heights of adjacent teeth are not necessarily the same. A device of this type gauges the height of one depth gauge partly in relation to the height of the cutting edge of an adjacent cutter link. The height of each depth gauge should be determined solely in relation to the cutter edge on the same cutter link.
Other devices have been developed for filing depth gauges. One example is found in the U.S. Pat. No. 4,412,463 to Beerens which discloses a guide for resting on the tip of a cutting edge and having apertures through which the depth gauge projects. A file is then placed on a plate and operated to file away the depth gauge until is it flush with the plate. U.S. Pat. No. 2,594,821 to Stone shows another gauge for filing saw chains. Such devices have the disadvantage that the guide or gauge must be held by one hand, while the file is operated by the other. This is awkward in practice. In addition, the devices are typically adapted only for use on specified types of chains.
U.S. Pat. No. 2,297,010 to Milano shows a saw filing device including a bar having clamps for securing the file.
The prior art does not offer a solution which permits simple filing in the conventional manner where both hands are used on the file and without the need for holding a depth gauge of some kind and which can be used on essentially all chains having a common pitch.